The invention relates to a method of manufacturing a semiconductor device, in which layer of photolacquer is formed on a semiconductor substrate, which layer contains as a photoactive component a diazo oxide and parts of which layer are irradiated by a first patterned irradiation, these irradiated parts then bring rendered poorly developable by an intermediate treatment, after which the lacquer layer is subjected to a second non-patterned irradiation and is then developed.
A photolacquer containing a diazo oxide as a photoactive component is a "positive" photolacquer because the parts thereof irradiated during a patterned irradiation are soluble in a developer. In the method mentioned in the opening paragraph, these irradiated parts of the photolacquer layer are again rendered poorly developable during the intermediate treatment so that they are not soluable or only very slowly soluble in a developer. After the second irradiation, the parts of the photolacquer layer not irradiated during the first irradiation are dissolved in a developer. The parts irradiated during the first irradiation then remain. Thus, a "negative" image is formed in the "positive" photolacquer layer.
It has been found that in the manner described above--also designated as image reversal --, lacquer tracks having very different profiles can be formed in a photolacquer layer. For example, tracks may be formed which are narrower at their bottoms tops than at their, while tracks may be formed which are wider at their tops than at their bottoms, and also tracks which at their tops must have the same width as at their bottoms. Especially the the last possibility renders this method particularly suitable for manufacturing semiconductor devices comprising a semiconductor substrate having a surface which is not flat, but which has a stepped topography. A photolacquer layer formed on such a surface will exhibit differences in thickness because lacquer has the tendency to form a layer having a flat surface. Above steps the photolacquer layer will be thinner than beside the steps on the surface of such semiconductor substrate. With the use of a pattern of lacquer tracks having a rectangular cross-section as a mask, a corresponding pattern of conductors can be etched into a conductive layer present on such a surface without undesired restrictions or shortcircuits being formed in these conductors.
From Proceedings of the International Conference on Microlithography "Microcircuit Engineering 84", 25-29Sept. 1984, pp.555-559 a method is known of the kind mentioned in the opening paragraph, in which the intermediate treatment that is carried is a thermal treatment. During the first patterned irradiation, indene carboxylic acid formed from diazo oxide present is then decarboxylated. This decarboxyation is catalysed by an organic base, such as imidazol, added the photolacquer. Thus, the parts of the photolacquer layer irradiated during the first irradiation are rendered poorly developable.
It has been found in practice that it is difficult to obtain the desired lacquer profiles have the same width at their tops as at their bottoms. Especially the time of development and the concentration of lye in the developer should be chosen with great care. If, for example, the time of development is too short, lacquer profiles are formed which are narrower at their tops than at their feet; if the time of development is too long, lacquer profiles are formed which are wider at their tops than at their feet. If the photolacquer is developed in a developer having a non-optimized lye concentration, lacquer profiles can be obtained, however, which have the same width at their tops as at their feet, but their width then deviates from the width of the part of the photolacquer irradiated during the first irradiation.